1. Field of the Invention
The present invention relates generally to a power supply installation for a direct current (dc) electric railroad and more specifically to a power supply installation by which an alternating current (ac) power is converted into a dc power before being supplied to electric cars as a powering source.
2. Description of the Prior Art
Usually, a plurality of dc substantions are installed at appropriate intervals along a railroad track. In these dc substations, a single or plural sets of converters are arranged. The dc power output side of the converter is connected to each of electric car power supply lines through each semiconductor breaker and the ac power input side thereof is directly connected in common with a powering bus bar. In other words, plural power supply circuits having power rectifiers and high-speed dc breakers are connected in parallel with each other between substations so as to constract a dc power supply installation.
On the other hand, the electric car power supply lines are divided into plural sections, and each of the above divided electric car power supply line is connected to a positive bus bar through a high-speed breaker provided for each electric car power supply line and the electric car rails are connected to a negative bus bar at each substation.
In the prior art power supply installation for a dc railroad using semiconductor breakers, however, there exist various drawbacks as follows: (1) When the dc disconnecting switch is required to be opened, a powering breaker and a regenerative breaker should both be opened. Under these conditions, since a potential difference will be generated at a dead section whenever an electric car passes over the dead section, an arc is inevitably generated at the dead section, so that an accident may occur. (2) In addition, when the regenerative breaker is open, if a regenerative electric car is running on the electric car power supply line, a potential difference will occur at the other dead sections not directly related to the dc disconnecting switch now being opened. (3) In case of a powering/regenerative bus bar accident, the power rectifier and the regenerative breaker should both be opened. Under these conditions, if the extension power supply current supplied from the adjacent substation is required to be interrupted by the regenerative breaker, it is necessary to increase the interrupt capability of the regenerative breaker. Otherwise, the adjacent substation for supplying the extension power should also be suspended, thus resulting in a wide power suspension over a long car track.
The arrangement of the prior art power supply installation for a dc railroad will be described in more detail hereinafter with reference to the attached drawing under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT.